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78 PCB007 MAGAZINE I SEPTEMBER 2021 Au and Pd (ENEPIG): Recommendations for Instrumentation (Detectors) and their Limitations; Michael Haller, Fischer Technology The thick ness specif ication for ENEPIG states: • Nickel: 3 to 6 µm [118.1 to 236.2 µin] at ± 4 sigma (standard deviations) from the mean • Palladium: 0.05 to 0.30 µm [2 to 12 µin] at ± 4 sigma (standard deviations) from the mean • Gold: minimum 0.030 µm [1.2 µin] at - 4 sigma (standard deviations) below the mean. No upper limit • All measurements to be taken on a nominal pad size of 1.5 mm x 1.5 mm [0.060 in x 0.060 in] or equivalent area e ENEPIG spec was amended in 2015. e amendment added an upper spec limit for immersion gold thickness. e thickness spec- ification for ENEPIG states: • Nickel: 3 to 6 µm [118.1 to 236.2 µin] at ± 4 sigma (standard deviations) from the mean • Palladium: 0.05 to 0.30 µm [2 to 12 µin] at ± 4 sigma (standard deviations) from the mean • Gold: minimum 0.030 µm [1.2 µin] at -4 sigma (standard deviations) below the mean, maximum 0.07 µm [2.8 µin] If thicker gold is a design requirement, alter- nate gold deposition methods should be used, like: • Electroless gold • Reduction assisted immersion gold (RAIG) All measurements to be taken on a nominal pad size of 1.5 mm x 1.5 mm [0.060 in x 0.060 in] or equivalent area. IPC-4552 Rev A, ENIG e IPC-4552 A, revised ENIG specification was issued in 2017. e revision added a new lower limit for the immersion gold and for the first time specified an upper limit. IPC 4552A also addressed nickel corrosion and specified a "Corrosion Chart." It also included a method for qualifying XRF equipment. e IPC-4552 A, ENIG Specification 2017: • e gold thickness shall be 1.6 (0.04 µm) to 4.0 µin (0.1 µm) • e upper limit of 4.0 µin must be strictly adhered to Corrosion Chart Examine the corrosion spikes (if any) on the ENIG surface with an optical microscope at 1000X magnification, for frequency and depth. ree classification levels: • Level 1: Acceptable (less than 10 spike defects with a depth <20% of the nickel deposit thickness) • Level 2: Disputable (spikes and depth > than Level 1 and < Level 3) • Level 3: Rejectable (>10 spike defects with >2 microns depth) is was the first time that nickel corrosion was addressed and 4552A put a stake in the ground. It became clear that the way the corrosion eval- uation was stated was problematic because it did not address frequency of occurrence. IPC-4552B was initiated in 2017 to address this deficiency. 4552B maintained the levels set in 4552A but added a method to quantify fre- quency of occurrence. 4552B introduced the term "Product Rating." Seven specified loca- tions in a plated through-hole, or five specified locations on a surface pad were examined for defects and their frequency of occurrence: 1. Product rating 0: Acceptable; No corrosion defects. 2. Product Rating 1: Acceptable; >60% of locations examined show Level 1 or less.